ATLANTA (AP) -- It's the season for state and county fairs, and health officials are reminding fairgoers to be careful around pigs because of a new flu spreading from the animals to people.

Officials say 29 human cases of the new strain of swine flu have been confirmed in the U.S. in the last year, most of them children.

Ten of the 12 cases confirmed this week were linked to the Butler County Fair in southwest Ohio, which ended last weekend.

Pigs get the flu, too, and can spread it to people. The Centers for Disease Control and Prevention has been tracking sporadic cases since last year, when the new strain was first seen in people. A concern: the new strain has a gene from the 2009 pandemic strain that might let it spread more easily than pig viruses normally do.

So far, that seems to be the case for pigs to people, but it hasn't been spreading easily from person to person - which is the greater concern.

It also has not been unusually dangerous. All of the recent cases were mild, as were most of the earlier illnesses.

But even regular flu can be a serious illness, so people should be careful if they're going be around pigs, said Dr. Joseph Bresee, the CDC's chief of influenza epidemiology.

Fairgoers are advised to wash their hands and avoid taking food and drinks into livestock barns. Pregnant women, young children, the elderly and people with weakened immune systems should be particularly careful.

With summer and fall fairs, "we're likely to see additional cases," Bresee told reporters during a teleconference Friday. He said work has begun on a vaccine for the new strain in case it ever becomes more of a threat.

Meanwhile, officials at state fairs in Ohio and Indiana say they'll be watching for any signs of swine flu. The Ohio State Fair sent home two pigs with the flu this week.